Phobias are irrational fears that become debilitating. A fear of heights that prevents someone from stepping on a step-stool or a fear of door knobs that prevents someone from opening a door can make life challenging. Inside of us there is a part of our nervous system that prioritizes our own survival. The freezing fear that stops of from stepping off the high dive board is the same one that would stop us from stepping off of cliff, however in the case of the diving board we can usually overcome that. A phobia is not one easily overcome by logical thinking.
Working to clear out a phobia will not remove the natural fear you have that is there to keep you safe and alive. Removing one's fear of heights will not make them long for bungee jumping, though certainly that might become something they choose to do. What removing the fear will do is allow you to choose, rather than being flooded with an emotional reaction that becomes debilitating.
Phobias such as those relating to insects, snakes, heights, speech anxiety, along with many others. Social Phobia is a bit more complicated, but that too is treatable.